Strokes are the third leading killer of adults in this nation after cancer and heart disease. Half the survivors suffer permanent incapacitating disabilities. Over 40 percent of the patients in chronic care are stroke victims, many destined to spend their lives in such a facility despite intensive rehabilitative efforts. Arteriosclerotic disease of the extracranial carotid arterial complex, the arteries to the skull from the aorta which are the principal blood suppliers to the head and neck, is responsible for almost half of all strokes. If individuals at high risk for stroke can be more easily identified, preventive treatment can be initiated since the extracranial carotid artery is surgically accessible.
Noninvasive testing of the extracranial carotid complex has become a widely accepted method of patient screening for carotid stenosis or "narrowing of the orifice." Because these outpatient tests have a high degree of accuracy, a physician can use them to identify patients with significant carotid stenosis and refer the patient to a hospital for angiography and appropriate treatment.
In the past decade, improved medical and surgical methods of stroke prevention have emerged. Noninvasive diagnostic tests have achieved a degree of accuracy which justifies their acceptance as indicators of individuals at risk for stroke. No patient should be evaluated by only one noninvasive test, however, as each test has strengths and liabilities. A battery of tests best provides an indication of the patient's risk of stroke.
Ocular pneumoplethysmography (OPG-Gee) measures the pressure of the ophthalmic artery, the first major branch of the internal carotid artery. A disparity between ophthalmic artery and brachial artery (main artery of the arm) pressures provides indirect evidence of stenosis. OPG-Gee is a safe noninvasive test which accurately identifies patients with hemodynamically significant carotid stenosis.
Carotid phonoangiography (CPA) enables the examiner to analyze sounds emanating from blood vessels. A microphone is placed at various positions on the neck over the cervical carotid complex. In normal blood flow the CPA tracing will show heart sounds with no high frequencies. However, when laminar blood flow breaks down into turbulent flow, bruits or arterial origin sounds can be detected. Turbulence leads to artery pressure fluctuations causing the vessel wall to vibrate. These bruits can be heard on the skin surface through CPA and recorded audibly and graphically.
Thermography is a noninvasive test which depicts the body's infrared energy in a visible format. A thermograph detects and collects infrared radiations from the skin. Thermographic instruments have been used increasingly to diagnose cerebrovascular disease. Thermographic evaluation of the extracranial carotid complex is quite accurate in identifying individuals with high stroke risk.
While skin temperature can be affected by ambient temperature, humidity, air flow, and radiation, subcutaneous blood flow in the carotid complex is unaffected by external stimuli, an important factor in facial thermograms. While most of the face is nourished by the external carotid arteries, the eye orbits and surrounding tissues receive blood primarily from the internal carotid arteries. A normal facial thermogram shows temperature symmetry in areas supplied by the left and right, internal and external carotid arteries. A color scale and a calibrated temperature source have been developed to define specific temperatures in these various areas. Internal carotid stenosis, resulting in reduced blood flow to the eye, typically causes a significant ipsilateral decrease in periorbital tissue temperatures. Thermography detects this temperature decrease, generating an abnormal heat pattern. Successful endarterectomy results in a resumed blood flow through the internal carotid artery which is demonstrated by temperature symmetry in subsequent facial thermograms.
Ultrasound is an important noninvasive diagnostic tool to evaluate blood flow in the carotid complex. Pulse-echo ultrasonography uses high frequency signals to identify blood vessel walls and indicate stenosis. However, calcific plaque may absorb ultrasound waves and atherosclerotic plaque may have acoustic qualities similar to blood, thus escaping detection.
Combining the pulse-echo system with Doppler ultrasound does allow analysis of both vascular anatomy and blood flow. Periorbital Doppler Ultrasonagraphy detects blood flow direction in the terminal branches of the ophthalmic artery. In addition, this test measures flow changes in response to compression of selected branches of the external carotid artery. The beam from the Doppler instrument strikes moving blood cells and is reflected; the Doppler shift is proportional to blood velocity. Increased blood flow velocity through an area of stenosis has a corresponding increase in the pitch of the Doppler signal. Incoming information on blood flow velocity can be presented for audio, wave-form, and image analysis.
Not only has noninvasive infrared thermography been used to identify patients with a high risk of stroke, its measurement of the temperatures of parts of the body provides indications of various diseases and problems and the patient's physical condition. Unusual temperature patterns on the surface of the skin may be an indication of infection, disease, compromise of peripheral or arterial circulation, inflammation due to sprains or arthritis, vasodilation due to regional block or a drug regimen, acute venous thromboses, or exposure to the environment.